The present invention relates to a mechanism and system for measuring the opening between the grasping fingers of a mechanical robot. The invention is particularly useful for robots of the type employed in automatic chemical and biological analysis machines which may be operated in a corrosive atmosphere.
In robot systems for chemical and biological laboratories, highly corrosive atmospheres may be encountered because of the use of chemical solvents and reagents. Robots for carrying out laboratory tests in chemical and biological laboratories are coming into increasing use. one such system in available from Perkin-Elmer Corporation, Main Avenue (MS-12), Norwalk, Conn. 06856, U.S.A. under the designation "Master Lab System". That system is computer controlled, and is capable of doing a long series of tests on samples contained in test tubes without the necessity for supervision. In the operation of that robot system opposed fingers must grasp each test tube for manipulation of that test tube and for moving the test tube from one position to another.
It is essential in these operations that the control system must have some signal to indicate the relative positions of the grasping fingers so that the fingers are opened sufficiently to embrace the test tube which is to be grasped before the test tube is grasped, and so that the system has signals which indicate when the fingers have been opened to release a test tube.
Up to the present time, one common method for obtaining the finger opening position signals is through the use of a potentiometer which has an electromechanical contact which slides over a resistor element to register different positions in terms of variation in the resistance of the potentiometer. This system generally works satisfactorily, but has some serious potential disadvantages. These include the mechanical wear between the electromechanical contact and the resistor element, and the prospect of corrosion of the electromechanical contacts in the corrosive atmosphere which is often encountered in chemical and biological laboratories.